Image sensor and fabricating method thereof

ABSTRACT

An image sensor and fabricating method thereof may include a semiconductor substrate, a plurality of photodiodes formed on and/or over the semiconductor substrate, a first insulating layer formed on and/or over the semiconductor substrate including the plurality of photodiodes, at least one metal line formed on and/or over the first insulating layer, a second insulating layer having a plurality of wells formed on and/or over the plurality of photodiodes, a plurality of color filters formed by embedding color filter layers in a plurality of the wells, and a plurality of microlenses formed on and/or over the color filters.

The present application claims priority under 35 U.S.C. 119 to KoreanPatent Application No. 10-2007-0123619 (filed on Nov. 30, 2007), whichis hereby incorporated by reference in its entirety.

BACKGROUND

Generally, an image sensor is a semiconductor device that converts anoptical image to an electric signal. Image sensors can be categorizedinto CCDs (charge coupled devices) and CMOS (complementary metal oxidesilicon) devices. Image sensors include a light receiving area having aphotodiode for sensing light and a logic area for processing the sensedlight into an electric signal which may be turned into data. Manyefforts are ongoing to raise light sensitivity.

FIG. 1 is a cross-sectional diagram of CMOS image sensor 1 showing alight receiving area including photodiodes 20 a, 20 b and 20 c.Referring to example FIG. 1, image sensor 1 may include a plurality ofphotodiodes 20 a, 20 b and 20 c, and a device isolation layer (shallowtrench isolation, or “STI”) 12 for isolating a plurality of thephotodiodes 20 a, 20 b and 20 c from each other. First and secondinsulating layers 30 and 34 may be formed over a semiconductor substrate10. A metal line 32 may be electrically connected to a logic area in thesecond insulating layer 34. A contact 36 may electrically connect themetal line 32 to another area. A color filter layer 42 including red(R), blue (B) and green (G) may be formed over the second insulatinglayer 34 opposite each of a plurality of the photodiodes 20 a, 20 b and20 c. A planarizing layer 44 may be formed over the color filter layer42, and a microlens 46 may be formed over the planarizing layer 44opposite the color filter layer 42 including red (R), blue (B) and green(G).

As the pixel pitch of a CMOS image sensor is reduced, a photodiode mayfail to be completely focused even if an optimal microlens is formed.This is because a condensable minimum spot size in an optimal focuscondition is the size of the airy disc, which is proportional to 1/NAand the focal distance. In this case, the NA (numerical aperture) meansthe aperture of an iris.

In a pixel in a CMOS image sensor, the NA corresponds to the pixel pitchand the focal distance corresponds to a metal line layer thickness. Toobtain a focal spot of the same size, the thickness of the metal linelayer should decrease in proportion to the decrease in pixel size in agiven CMOS image sensor. However, the image sensor structure reaches adesign limitation when the metal line is required to have a thicknesssmaller than a minimum thickness requirement dictated by other designrules. Hence, a pixel pitch limit is generated, preventing furtherreductions in pixel size. According to a computer simulated studyresult, the above optical limit is estimated to be reached in a pixel ofabout 1.75 μm.

SUMMARY

Embodiments relate to a semiconductor device, and more particularly, toa CMOS image sensor and fabricating method thereof. Embodiments relateto an image sensor and fabricating method thereof, by which sensitivityof the image sensor can be raised by increasing light condensingefficiency of a microlens by effectively decreasing a vertical distancebetween a photodiode and the microlens of the image sensor. Embodimentsrelate to an image sensor and fabricating method thereof, by which lightcan be condensed at the same level of other image sensors using amicrolens having a greater thickness than that of other microlenses.

Embodiments relate to a method of fabricating an image sensor which mayinclude providing a semiconductor substrate, forming a plurality ofphotodiodes over the semiconductor substrate, forming a first insulatinglayer over the semiconductor substrate including the plurality ofphotodiodes, forming at least one metal line over the first insulatinglayer, forming a second insulating layer over the first insulating layerincluding the at least one metal line, forming a plurality of wells overthe plurality of photodiodes by etching the second insulating layer,filling the plurality of wells with color filter layers to form aplurality of color filters, and forming a plurality of microlenses overthe plurality of color filters.

Embodiments relate to an image sensor which may include a semiconductorsubstrate, a plurality of photodiodes formed over the semiconductorsubstrate, a first insulating layer over the semiconductor substrateincluding the plurality of photodiodes, at least one metal line formedover the first insulating layer, a second insulating layer having aplurality of wells formed over the plurality of photodiodes, a pluralityof color filters formed by embedding color filter layers in a pluralityof the wells, and a plurality of microlenses formed over the colorfilters.

Embodiments relate to a method of fabricating an image sensor which mayinclude forming a plurality of photodiodes over a semiconductorsubstrate, forming a first insulating layer over the semiconductorsubstrate including the plurality of photodiodes, forming at least onemetal line over the first insulating layer, forming a plurality of wellsin the first insulating layer over the plurality of photodiodes, forminga plurality of color filters by disposing color filter layers in theplurality of wells, forming a second insulating layer over the firstinsulating layer including the at least one metal line and the pluralityof color filters, and forming a plurality of microlenses over the colorfilters.

Embodiments relate to an image sensor which may include a semiconductorsubstrate, a plurality of photodiodes formed over the semiconductorsubstrate, a first insulating layer including a plurality of etchedwells over the plurality of photodiodes, at least one metal line overthe first insulating layer, a plurality of color filters formed by colorfilter layers formed in the plurality of etched wells, a secondinsulating layer over the first insulating layer including the at leastone metal line and the plurality of color filters, and a plurality ofmicrolenses formed over the plurality of color filters.

Accordingly, embodiments may provide the following effects and/oradvantages. Unlike other CMOS image sensors, a plurality of wells formedwithin a second insulating layer may be filled up with color filters. Amicrolens is directly formed without forming a planarizing layer betweenthe color filters. Therefore, sensitivity of the image sensor can beoptimized by increasing light condensing efficiency of a microlens byeffectively decreasing a vertical distance between a photodiode and themicrolens of the image sensor. In addition, light can be condensed atthe same level of others using a microlens having a greater thicknessthan that of other microlenses. Therefore, a thickness margin forforming a microlens can be enhanced in a microlens forming process.

DRAWINGS

Example FIG. 1 is a cross-sectional diagram of a CMOS image sensor.

Example FIGS. 2A to 2F are cross-sectional diagrams for a method offabricating an image sensor according to embodiments.

Example FIGS. 3A to 3D are cross-sectional diagrams for a method offabricating an image sensor according to embodiments.

DESCRIPTION

Example FIGS. 2A to 2F are cross-sectional diagrams for a method offabricating an image sensor according to embodiments.

Referring to example FIG. 2A, a plurality of photodiodes 20 a, 20 b and20 c may be formed over semiconductor substrate 10. A device isolationlayer (shallow trench isolation) 12 may then be formed to isolatephotodiodes 20 a, 20 b and 20 c from each other. Alternatively, afterdevice isolation layer 12 has been formed in semiconductor substrate 10,a plurality of photodiodes 20 a, 20 b and 20 c may be formed. Firstinsulating layer 30 may be formed of a transparent substance on and/orover the semiconductor substrate 10 having a plurality of photodiodes 20a, 20 b and 20 c formed therein. A trench may be formed in a portion offirst insulating layer 30 by a photolithographic etch using a mask. Thetrench may be filled with an electrically conductive substance (e.g.,Al, Cu, etc.) to form contact 36. Metal line 32 connected to anotherarea may be formed on and/or over first insulating layer 30, overlappingcontact 36. Metal line 32 and contact 36 may play a role in electricallyconnecting logic and light-receiving areas together. Second insulatinglayer 34 may be formed by depositing (coating) a transparent substanceon and/or over first insulating layer 30 having metal line 32 formedthereon.

Referring to example FIG. 2B, photoresist pattern 40 may be formed onand/or over second insulating layer 34 to correspond to metal line 34.Photoresist pattern 40 may be patterned to expose a partial area ofsecond insulating layer 34 corresponding to photodiodes 20 a, 20 b and20 c. In particular, photoresist pattern 40 may be patterned to formcolor filters corresponding to photodiodes 20 a, 20 b and 20 c,respectively.

Referring to example FIG. 2C, a plurality of wells 42, 44 and 46 may beformed to a prescribed depth in second insulating layer 34 by etchingsecond insulating layer 34 using photoresist pattern 40 as an etch mask.For instance, each well 42, 44 and 46 may be formed between the metallines. The depth of each of well 42, 44 and 46 may be in a range betweenapproximately 100 nm to 1,000 nm, and more particularly, in a rangebetween approximately 600 nm to 700 nm, which may correspond to thethickness of the color filter layer.

Referring to example FIG. 2D, color filter 50 may be formed in each well42, 44 and 46 of second insulating layer 34 to correspond to eachphotodiode 20 a, 20 b and 20 c. For instance, a blue color filter, agreen color filter and a red color filter can be provided in wells 42,44 and 46 to correspond to photodiodes 20 a, 20 b and 20 c,respectively. With regard to photodiodes 20 a, 20 b and 20 c, lighttraveling through the green (G) color filter may be received by firstphotodiode 20 a, light traveling through the blue (B) color filter maybe received by second photodiode 20 b, and light traveling through thered (R) color filter may be received by third photodiode 20 c.

Referring to FIG. 2E, microlenses 60 a, 60 b and 60 c may be formed onand/or over color filter layer 50 and correspond to color filters 50,respectively. Microlenses 50 a, 60 b and 60 c may be formed having ahemispherical cross-section by performing a reflow process at atemperature in a range between approximately 120° C. to about 200° C.Microlenses 60 a, 60 b and 60 c may be hardened by applying UV raythereto.

Referring to example FIG. 2F, protective layer 70 may be formed onand/or over microlenses 60 a, 60 b and 60 c to protect from moisture andscratches. Since a substance of protective layer 70 may have arefraction index (e.g., in a range between approximately 1.6 to 1.7)almost equal to that of microlenses 60 a, 60 b, 60 c for visible raywavelengths, optical refraction may be minimized between protectivelayer 70 and microlenses 60 a, 60 b, 60 c.

Comparing the image sensor fabricated by the method according toembodiments to the image sensor shown in example FIG. 1, the colorfilter layers may be embedded in the second insulating layer. Theplanarizing layer formed over the color filter layers may be omitted.Therefore, embodiments may reduce the distance between photodiodes 20and microlens 60 in a range between approximately 1 μm to 2 μm.Therefore, the photodiode may be in substantially complete focus with athicker microlens than other microlenses. Since the distance betweenphotodiodes 20 and microlenses 60 may be reduced, light loss may bedecreased and a light condensing function may be relatively increased,whereby sensitivity of the image sensor can be maximized.

Example FIG. 2F is a cross-sectional diagram of a light-receiving areaof an image sensor fabricated by a method according to embodiments.Referring to example FIG. 2F, an image sensor may include a plurality ofphotodiodes 20 a, 20 b and 20 c provided to a semiconductor substrate toconvert incident light to an electric signal. First insulating layer 30may be formed on and/or over semiconductor substrate 10 havingphotodiodes 20 a, 20 b and 20 c. Metal line 32 may be formed on and/orover first insulating layer 30. Second insulating layer 34′ may beformed with a plurality of wells on and/or over first insulating layer30 including metal line 32. Color filter layers 50 may be provided in aplurality of the wells opposite the plurality of photodiodes 20 a, 20 band 20 c, respectively. A plurality of microlenses 60 a, 60 b and 60 cmay be provided to correspond to color filter layers 50, respectively.Accordingly, the image sensor of embodiments shown in example FIG. 2Fdiffers from the image sensor shown in example FIG. 1 in that the colorfilters may be embedded in the wells of the second insulating layer.Microlenses 60 a, 60 b and 60 c may be directly formed without formingthe planarizing layer between color filter layers 50. Therefore,embodiments reduce the distance between microlens 60 a, 60 b, 60 c andphotodiode 20 a/20 b/20 c in a range between approximately 1 μm to about2 μm. Accordingly, light condensing efficiency of the microlens may beincreased, thereby raising the sensitivity of the image sensor.Moreover, since embodiments achieve the light condensing ability at thesame level of other using a thicker microlens than the other microlens,the allowable margin of variation in the thickness of the microlens canbe enhanced during formation of the microlens.

Example FIGS. 3A to 3D are cross-sectional diagrams for a method offabricating an image sensor according to embodiments, in which steps upto forming metal line 32 are essentially the same as those illustratedand described in example FIGS. 2A to 2F.

Referring to example FIG. 3A, plurality of wells 310 may be formed to aprescribed depth in first insulating layer 30, on and/or over whichmetal line 32 is formed, by photolithography using a mask. Wells 310 maybe formed opposite photodiodes 20 a, 20 b and 20 c, respectively. Thedepth of each of well 310 may be in a range between approximately 100 nmto 1,000 nm, and more particularly, in a range between approximately 600nm to 700 nm, which may correspond to a thickness of a color filterlayer.

Referring to example FIG. 3B, each well 310 formed in first insulatinglayer 30 may be filled with color filter layer 320. Referring to exampleFIG. 3C, second insulating layer 330 may be formed with a transparentsubstance on and/or over first insulating layer 30 including metal line32 and color filter layers 320.

Referring to example FIG. 3D, microlenses 340 may be formed on and/orover second insulating layer 330 and corresponding to color filterlayers 320. Protective layer 350 may be formed on and/or overmicrolenses 340 to protect microlenses 340 and/or color filter layers320 from moisture and scratches. Accordingly, an image sensor accordingto embodiments may include plurality of photodiodes 20 a, 20 b and 20 cprovided on and/or over semiconductor substrate 10 to convert incidentlight to an electric signal. First insulating layer 30 may be formed onand/or over semiconductor substrate 10 with photodiodes 20 a, 20 b and20 c formed thereon and/or thereover. Metal line 32 may be formed onand/or over first insulating layer 30. Color filter layers 320 may beembedded in a plurality of wells formed by etching first insulatinglayer 30 opposite a plurality of photodiodes 20 a, 20 b and 20 c. Secondinsulating layer 330 may be formed on and/or over first insulating layer30 including metal line 32 and the filer layers 320. A plurality ofmicrolenses 340 may be formed on and/or over second insulating layer 330to correspond to color filter layers 320. The image sensor according toembodiments can further include another protective layer formed onand/or over microlenses 340 to protect microlenses 340 and/or colorfilter layers 320 from moisture or scratches. The image sensor shown inexample FIG. 3D according to embodiments, like the image sensor shown inexample FIG. 2F, can reduce the distance between the microlenses andcorresponding photodiodes. Accordingly, light condensing efficiency ofthe microlens may be increased, thereby raising the sensitivity of theimage sensor.

Although embodiments have been described herein, it should be understoodthat numerous other modifications and embodiments can be devised bythose skilled in the art that will fall within the spirit and scope ofthe principles of this disclosure. More particularly, various variationsand modifications are possible in the component parts and/orarrangements of the subject combination arrangement within the scope ofthe disclosure, the drawings and the appended claims. In addition tovariations and modifications in the component parts and/or arrangements,alternative uses will also be apparent to those skilled in the art.

1. A method comprising: providing a semiconductor substrate; and thenforming a plurality of photodiodes in the semiconductor substrate; andthen forming a first insulating layer over the semiconductor substrateincluding the plurality of photodiodes; and then forming at least onemetal line over the first insulating layer; and then forming a secondinsulating layer over the first insulating layer including the at leastone metal line; and then forming a plurality of wells over the pluralityof photodiodes by etching the second insulating layer; and then fillingthe plurality of wells with color filter layers to form a plurality ofcolor filters; and then forming a plurality of microlenses over theplurality of color filters.
 2. The method of claim 1, further comprisingforming a protective layer over the microlenses.
 3. The method of claim2, wherein forming the plurality of wells comprises etching the secondinsulating layer to a depth in a range between approximately 600 nm to700 nm.
 4. The method of claim 2, wherein forming the protective layercomprises forming the protective layer to have substantially the sameindex of refraction for light in the visible spectrum as that of themicrolenses.
 5. The method of claim 1, wherein forming the microlensescomprises forming the microlenses having hemispherical cross-sections byperforming a reflow process at a temperature in a range betweenapproximately 120° C. to about 200° C.
 6. An apparatus comprising: asemiconductor substrate; a plurality of photodiodes formed in thesemiconductor substrate; a first insulating layer formed over thesemiconductor substrate including the plurality of photodiodes; at leastone metal line formed over the first insulating layer; a secondinsulating layer formed over the first insulating layer including the atleast one metal line; a plurality of wells formed over and correspondingspatially to the plurality of photodiodes; a plurality of color filtersformed in a respective one of the plurality of the wells; and aplurality of microlenses formed over and spatially corresponding to thecolor filters.
 7. The apparatus of claim 6, further comprising aprotective layer formed over the microlenses.
 8. The apparatus of claim7, wherein the protective layer is made of a material which protects thecolor filter layers and the microlenses from moisture and scratches. 9.The apparatus of claim 7 wherein each of the protective layer and themicrolens is made of a material having substantially the same index ofrefraction for light in the visible spectrum.
 10. The apparatus of claim6, wherein the wells in the second insulating layer have a depth in arange between approximately 600 nm to 700 nm.
 11. The apparatus of claim6, further comprising a contact formed in the first insulating layer andelectrically connected to the at least one metal line.
 12. A methodcomprising: forming a plurality of photodiodes in a semiconductorsubstrate; and then forming a first insulating layer over thesemiconductor substrate including the plurality of photodiodes; and thenforming at least one metal line over the first insulating layer; andthen forming a plurality of wells in the first insulating layer over andspatially corresponding to the plurality of photodiodes; and thenforming a plurality of color filters by forming color filter layers inthe plurality of wells; and then forming a second insulating layer overthe first insulating layer including the at least one metal line and theplurality of color filters; and then forming a plurality of microlensesover the color filters.
 13. The method of claim 12, wherein forming theplurality of wells comprises etching the first insulating layer to adepth in a range between approximately 600 nm to 700 nm.
 14. The methodof claim 12, wherein forming the plurality of wells comprises etchingthe first insulating layer to a depth in a range between approximately100 nm to 1,000 nm.
 15. The method of claim 12, further comprisingforming a protective layer over the microlenses.
 16. The method of claim15, wherein forming the protective layer comprises forming theprotective layer to have substantially the same index of refraction forlight in the visible spectrum as that of the microlenses.
 17. The methodof claim 12, further comprising, after forming the first insulatinglayer: forming a trench in a portion of the first insulating layer; andthen filling the trench with an electrically conductive substance toform a form contact.
 18. The method of claim 17, wherein theelectrically conductive substance comprises at least one of aluminum andcopper.
 19. The method of claim 17, wherein the trench is formed by aphotolithographic etch using a mask.
 20. The method of claim 17, whereinthe at least one metal line is electrically connected to the contact.